Method for increasing the flex life of synthetic leather and product produced thereby



Dec. 22, 1970 J. D. HEFLEY ET AL r 3,549,415

METHOD FOR INCREASING THE FLEX LIFE OF SYNTHF'TI'C LI'IA'IIWR AND PRODUCT PRODUCED TI-IEREBY Filed May 24, 1967 INVENTOR JACK D. HEFLEY' W ILL BAM H. WEST ATTORNEY United States Patent US. Cl. 161-159 7 Claims ABSTRACT OF THE DISCLOSURE A method for increasing the flex life of a poromeric material and/ or the fibrous substrate used in poromeric materials by after treating the material with a substantially non-volatile lubricant and the product produced thereby. The process is particularly applicable to polyurethane containing poromerics.

BACKGROUND OF THE INVENTION Synthetic leather, commonly referred to as poromeric material, has recently become a highly desirable and adequate substitute for leather. In many instances, these materials are superior to leather, particularly in uniformity, aesthetic values and the like characteristics. However, it is desirable to increase certain other characteristics, particularly durability as measured in the flex life of the product. While durability or flex life is quite high for many purposes, being measured in the millions of flexes, it is desirable to greatly, increase this flex life, particularly for certain uses such as footwear.

One of the difliculties involved in increasing the flex life resides in the normally desirable multi-component construction of the poromeric material. Such construction comprises a plurality of layers of different substances. conventionally, a coating composition is applied to a flexible substrate and a top coating is placed over the coating composition. The application of a plurality of coatings greatly increases the heat generated in flexing the material. The poromeric material thus has built in means for self-degradation. This is particularly true when polymers of relatively low degradation temperatures, such as polyurethane, are used as the polymeric coating material. While the polyurethanes are most susceptible to heat degradation, they also have withstood attempts to reduce the internal frictional forces therein due to the fact that most lubricants are also release agents for polyurethanes and therefore the incorporation of a lubricant into a poromeric component results in the inability to firmly adhere the original or subsequent polyurethane coatings in the construction of multi-component poromeric materials.

It is an object of the present invention to provide a method for reducing the frictional forces and consequent heating effect in poromeric materials, thereby increasing the flex life of the resulting poromeric material. It is another object of the present invention to provide a poromeric material of greatly increased flex life. These and other objects will become apparent to those skilled in the art from the description of the invention which follows.

SUMMARY OF THE INVENTION In accordance with the invention, a process is provided for increasing the flex life of a poromeric material com- 3,549,475 Patented Dec. 22, 1970 "ice,

prising applying a lubricating amount of a substantially nonvolatile lubricant to a porous poromeric structure comprising a flexible porous substrate coated with a porous elastomeric material thereby impregnating said material with said lubricant. The invention is particularly applicable to impregnating an entire poromeric material having a fibrous substrate coated with a porous, flexible polyurethane coating composition.

The present invention provides a simplified means of greatly increasing the flex life of poromeric materials with a minimum of expense and simplicity of operation. Using the method of the present invention, a poromeric material is produced having a flex life of 2, 3 or more times that of similar untreated poromeric materials. The treatment of the entire poromeric structure with the lubricant greatly reduces the frictional forces and the internal structural stresses which produce a heating effect which in turn leads to the premature degradation of the poromeric structure.

Because the invention is preferably applied to a completed poromeric material the invention will be described more particularly in this respect although it is to be noted that the invention can be effected in certain instances with respect to the substrate material with correspondingly good results.

The invention will be described more fully by reference to the drawing which is a sectional view of a typical poromeric material A poromeric material 10 is normally comprised of a flexible substrate 12, a flexible polymeric coating composition 14 which is water-vapor permeable and, as is normally desired, a flexible polymeric topcoat 16 is applied over the water-vapor permeable coating. The topcoat is often a non-porous flexible polymer of the same or different composition as the porous coating composition.

The present invention is applicable to poromeric materials in general. However, the invention is more particularly applicable to poromerics having fibrous substrates and polyurethane coatings. Therefore, the invention will be described more fully with respect to these materials although this further description is not to be considered as limiting the scope of the invention.

The flexible substrate on which the polymeric coating is applied may be most any flexible sheeting such as paper, plastic and the like, but preferably the substrate is porous to water vapor and more preferably the substrate is a fibrous composition which may be woven, knitted, braided, twisted, nonwoven or the like, natural, that is, animal, vegetable or mineral fibers, or synthetic fibers and mixtures thereof. The particular substrate used is not critical to the invention although the substrate is preferably a Water-vapor permeable fibrous material. Therefore, a substrate of fibrous materials such as cotton, flax, jute, silk, wool, asbestos, nylon, rayon, acetate, triacetate, polyester, polyamide, polyethylene, polypropylene, polyurethane, polyvinyls, acrylics and the like fibers can be used as well as cellulose based substrates. The substrates may be filled or bonded or nonfilled with a resinous material such as a polyester, polyurethane, latex or the like polymeric material. Also, if desired, the fibrous material can be laminated with other fibrous materials or with a synthetic plastic sheet material.

The most preferred substrate is a nonwoven composition of synthetic fibers such as polyester staple and polypropylene staple needled to a high density such as that obtained in needling a batting with about 1000 to 5000 punches per square inch. The needled substrate can be subsequently shrunk, if desired, and/ or impregnated with a bonding agent. The prepared substrate is preferably of a thickness of about 0.005 to about 0.3 inch thick and more preferably about 0.01 to 0.1 inch thick. The substrate has a tensile strength of about to 1600 pounds per square inch or more, and more preferably about 900 to 1200 pounds per square inch.

The denier of the structural fiber component can vary widely. It can be as great as about 30 denier per filament or more but normally, fibers of about 0.5 to 3 denier per filament are preferred because they are easier to handle and give a product of greater pliability, toughness and scuff resistance.

The flexible polymeric coating used, often referred to as an elastomer, may be any of numerous plastic materials commonly used in the manufacture of synthetic leather and similar products. Many different polymers are utilized for this purpose, all of which are well known in the art. Such materials retain a leather-like flexibility after final cure and thus are best defined as elastomeric or flexible polymers. The term polymeric or elastomer as used herein is used in its broad sense to include various flexible polymers such as polyesters, polyethers, vinyls such as polyvinyl chloride, polyvinylidene chloride, vinyl chloridevinylacetate copolymers, vinyl chloride-vinylidene chloride copolymers and mixtures of the same and the like. In addition, other suitable polymers include copolymers of vinyl chloride or other vinyl halides with monomers such as acetate, vinylidene chloride, diethyl maleate and vinyl acetals such as vinyl butyral chloride. However, because the preferred polymeric coating is a polyurethane composition, the invention will be described more fully with respect to the polyurethanes.

The polyurethane elastomers utilized in the present invention, as well as the other polymeric materials are those which can be cured or hardened to a flexible state by the the removal of solvent, cooling, polymerizing and the like as well as combinations thereof.

A preferred polymeric coating composition useful with the present invention is a polyurethane elastomer made by reacting an organic diisocyanate with an active hydrogen containing polymeric material such as a polyalkylene ether glycol, a hydroxyl containing polyester or a polyesterpolyamide to produce an isocyanate-terminated polyurethane prepolymer and reacting the resulting prepolymer with a chain-extending compound having two active hydrogen atoms bonded to amino-nitrogen atoms. Hydrazine and N-methyl-aminobis-propylamine are typical chain extenders. However, others which are useful include dimethylpiperazine, 4-methyl m phenylene diamine, mphenylene-diamine, 1,4-diamino-piperazine, ethylene diamine and mixtures thereof. Also, thermoplastic or one package thermal processable elastomeric polyurethanes which form polymeric structures through hydrogen bonding can be used.

The polyurethane elastomer can be prepared by first mixing a molar excess of the diisocyanate with the active hydrogen containing polymeric material and heating the mixture at about 50120 C. until the prepolymer is formed. Or, the diisocyanate can be reacted with a molar excess of the active hydrogen containing polymeric material, and the reaction product capped by reacting it with more diisocyanate to form the prepolymer. Numerous variations of these basic reactions are known and can be used in the present process.

Aromatic, aliphatic and cycloaliphatic diisocyanates or mixtures thereof can be used in forming the prepolymer. Such diiosocyanates are, for exampe, tolylene-2,4-diisocyanate, tolylene-Z,6-diisocyanate, m-phenylene diisocyanate, biphenylene-4,4-diisocyanate, methylene bis(4- phenyl isocyanate), 4-chloro-l,3-phenylene diisocyanate, naphthalene-1,S-diisocyanate, tetramethylene-l ,4 diisocyanate, hexamethylene-1,6-diisocyanate, decamethylene-l, -diisocyanate, cyclohexylene-1,4-diisocyanate, methylene bis(4-cyclohexyl isocyanate) and tetrahydronaphthalene diisocyanate. Arylene diisocyanates, that is, isocyanates in which the isocyanate groups are attached to an aromatic ring, are preferred. In general they react more readily than do alkylene diisocyanates.

Polyester polyamides and polyalkyleneether glycols are the preferred active hydrogen containing polymeric materials for the prepolymer formation. The polyesters and polyester polyamides are formed by conventional processes such as by reacting acids, esters or acid halides with glycols. Acids for preparing such polyesters are, for example, succinic, adipic, suberic, sebacic, terephthalic and hexahydroterephthalic acids and the alkyl and halogen substituted derivatives of these acids.

As stated herein, the polymeric coating composition is applied so as to form a porous coating over the flexible substrate. Various techniques can be utilized in this process. One technique particularly applicable to polyurethanes is to incorporate a small amount of water or blowing agent such as Freon into the polymer prior to final cure, thus foaming the polymer during the initial curing step. Another method which is often preferred is to incorporate a finely divided solid material into the polymeric coating prior to coating the substance. The finely divided solid material is one which is insoluble in the coating composition and nondeleterious to and nonreactive with the polymer or solvent therefor. Also, the solid material is one which can be readily removed from the polymer after curing by various means such as decomposition, volatilization, solubilization or the like. The most preferred finely divided solid materials incorporated into the coating composition are water or alcohol soluble compounds which do not fuse, decompose or volatilize at the temperature utilized to cure the coating composition. Curing temperatures are normally below about degrees centigrade and therefore useful solid materials can be any of numerous substances. However, the preferred materials are inorganic materials such as salts or mixtures of salts, especially alkali metal salts such as sodium and potassium chlorides, bromides, sulfates, ammonium sulfates and the like, of which sodium chloride is the most preferred. However, materials which volatilize above the curing temperature and below the polymer degradation temperature, such as ammonium acetate can also be used with correspondingly good results.

The solid material is preferably of a US. Standard sieve number less than about 60 and more preferably less than about 200 and most preferably that which passes through a US. Standard Sieve Number 325. The solid particles are incorporated into the polymeric coating material by various means such as by intimately mixing the solid particles and the polymer in a proportion by weight of about 1:1 to 6:1 and more preferably in a proportion of about 2:1 to 5:1 salt to polymer on the solid basis. The particular amount of solid material used and the particular size thereof effects the water-vapor permeability of the resulting product. A greater content of finely divided material increases the porosity of the finished product.

The prepared coating composition is applied to the flexible substrate by any of numerous methods, including spraying, brushing, spreading and the like. For example, particularly desirable methods are the floating knife method, calendering, cast-coating, roller-coating and the like. One of the more preferred methods is to use a doctor blade technique whereby the composition is applied as a viscous resin which may or may not contain a solvent depending on the temperature of application, the polymer used and the preferred viscosity for such application.

The application can be effected in a single or multitude of successive applications or coatings with or without partial or complete cure between successive coatings. A preferred method of application is by successive coatings of about 1 to 3 mils per coating with partial curing between each successive layer. However, various other techniques are equally applicable, the particular technique utilized depending primarily on the polymer coating composition used. However, it is preferred that the coating be applied to the substrate to achieve a finally cured coating of a thickness of about 3 to 100 mils and more preferably of about to 50 mils and more preferably about 30 mils.

As may be desired for the particular end use of the polymeric material made, a topcoating may be applied which normally does not account for more than about 10 percent of the coating composition applied to the substrate. The topcoating is preferably of the same material as the polymeric coating but is applied so as to form a continuous nonporous film. Thus, salt, blowing agents and the like are normally not incorporated into the topcoat formulation. The thin topcoating does not greatly limit water-vapor permeability while enhancing scuff resistance and abrasion. The finally prepared poromeric material is then lubricated by impregnating the entire poromeric structure with a lubricant.

The term lubricant is used herein in its broad and conventional sense as being a substance which reduces friction, heat and wear when introduced as a film between solid surfaces. These lubricants used are further described as being of a viscosity range from about one stoke to a grease-like consistency at room temperatures. More particularly, the lubricants are substantially nonvolatile liquids. Typically, these compositions are refined petroleum or mineral oils, synthetic hydrocarbon lubricants, polyglycols, polyglycol ethers and esters, monoesters and glycerides, hydrocarbon halides, fluorocarbons and silicone oils, preferably of the water insoluble type such as organo siloxane polymers such as methyl and phenyl polysiloxanes, having viscosities in the range of less than about 1 stoke up to a grease-like consistency. In addition, various fatty chain containing materials such as fatty esters, acids, amides, amines, imines, alcohols, nitriles, soaps, salts, epoxies and the like having fatty chains of 8 to about 30 carbon atoms can be used alone or in combination with other lubricants or as additives. The more preferred lubricants are particularly characterized as being relatively nonreactive, particularly with respect to degradation through oxidation under the conditions to which the polymeric material would be expected to be submitted, and substantially nonvolatile at room temperatures. Thus, the vapor pressure of the preferred lubricating oils is sufficiently low so that evaporative losses at room temperatures are negligible even over extended periods of time.

The most preferred compositions are the silicon and refined mineral oils. The mineral or petroleum oils which are particularly useful are those oils which are classified as spindle oils, neutral oils, red and pale oils, bright stocks and steam-cylinder oils. The more preferred petroleum oils are those of an S.A.E. 5 to S.A.E. 70- rating and most preferably, viscosity stabilized detergent oils such as -20W, 5-30W and the like. Thus, petroleum oils containing various additives and stabilizers are highly desirable.

In addition to the highly preferred petroleum oils, silicone oils, often referred to as polysiloxaues, are also particularly useful in the present invention. Typical of the silicone oils is dimethyl silicones, phenylmethyl silicones, linear methylsiloxane polymers, polymethylphenylsiloxane, cyclic polysiloxanes, 3,3 diphenyltrisiloxane and the like. These oils normally have viscosities in the range of about 1 to 1000 stokes or more.

Other lubricants useful in the present invention are synthetic hydrocarbons such as polymerized olefins including polymerized ethylene, propylene, butylene and the like of a molecular weight of about 250 to about 50,000. Polyglycols such as polyethylene glycol and polypropylene glycol and more particularly their water insoluble esters and ethers are useful lubricants within the scope of the invention. Monofatty esters of 12 to 30 carbon atoms such as ethylpalmitate, ethylstearate and their respective acids such as stearic acid, palmitic acid and the like can also be used as well as the respective amines, imines, amides, nitriles, epoxies, soaps and salts. Many of these latter compounds are most favorably used as additives for the petroleum oils. In addition to the monoesters, the respective fatty glycerides and diesters can be used, particularly aliphatic diesters such as ethylene glycol dilaurate, cyclic diesters and triesters of phosphoric acid, particularly aliphatic orthophosphates. While most of the compounds described are aliphatic in nature, aromatic lubricating compounds can also be used. However, the gen erally linear nature of the aliphatic materials generally makes them more acceptable as lubricants and therefore they are normally preferred.

The oils are applied to the polymeric composition in a lubricating amount. This amount ranges from about 0.01 percent to about 10 percent or more by weight of the poromeric material. More preferably, the lubricant is ap plied in the range of about 0.05 to about 2 percent by weight of the poromeric material and most preferably in the range of about 0.1 to 1.5 percent by weight of the poromeric material. In the most preferred range, the presence of the oil is not readily detected by touch or feel, and the oil does not exude from the poromeric material on extensive use. However, with correspondingly higher concentrations, depending upon the particular lubricant used, correspondingly improved flex lifes are obtained.

The lubricant is applied to the poromeric material, preferably in a diluted concentration in a volatile solvent. The porous nature of the poromeric substrate and coating composition readily lends itself to complete impregnation with the lubricant. The application of the lubricant can be made by various methods such as by submersion, brushing, spraying or otherwise soaking the poromeric material with the solvent thinned lubricant. The solvent is sub sequently volatilized from the poromeric material, thus leaving the oil evenly distributed throughout the poromeric material. The particular method of impregnating the poromeric material is not critical. However, the use of a solvent to thin the lubricant provides a ready means for thorough distribution of the lubricant throughout the poromeric material in a controlled manner.

The invention will be described more fully by reference to the examples which illustrate certain preferred embodiments of the present invention. Unless otherwise indicated, all parts and percentages are by Weight.

EXAMPLES 1 THROUGH 5 A poromeric material was made in accordance with the present invention by forming a flexible substrate of batting comprising a mixture of 1.5 denier per filament of 1%. inch drawn polyester staple and 1.8 denier per filament of 1 inch drawn polypropylene staple. The blend was fed into a garnet to form an intimately blended web of a density of 24 ounces per square yard. The web was passed through a needle puncher wherein the web was needled to about 4000 needle punches per square inch. The produced batting was then impregnated with a latex butyl-melamine formaldehyde bonding agent to achieve a 30 percent weight by solids pickup based on the dry fiber weight. The finally prepared batting was of a thickness of about 0.026 inch.

An elastomeric coating composition was then prepared by mixing 167 parts of sodium chloride with 116.4 parts of Daltoflex 18, a polyester polyamide diisocyanate prepolymer manufactured by ICI, diluted in methylethylketone to 27 percent solids. Subsequently, 3 parts of Suprasec K2 diisocyanate curing agent for the prepolymer at 40 percent solids in methylethylketone and 6 parts of 1.8 percent solution of dimethylphenethylamine in methylethylketone were mixed with the prepolymer composition. The sodium chloride was of a finel divided particle size.

The salt addition resulted in a salt-polymer ratio of about 4: 1 by weight of solids.

The prepared salt-polymer mixture was then applied to the prepared fibrous substrate in a plurality of applications to attain a total of about 30 mils of dry polymeric coating. The coated product was then divided into a control and test samples for the application of a lubricant in accordance with the present invention.

A viscosity stabilized high detergent 20-20W motor oil diluted, as shown in Table I, with methylethylketone was applied to the poromeric material by immersing the poromeric in the diluted motor oil for minutes. By controlling the dilution rate, that is, the percentage of oil in the solution and the time of immersion, the oil picked up by the poromeric material was readily adjusted. A 10 minute immersion corresponded to an oil pick-up equal to the oil dilution. On removing the poromeric material from the immersion bath the excess solution was drained off and the solvent flashed off. The material was further dried for 1 hour in an oven at 160 degrees Fahrenheit and subsequently aged at room temperature and humidity for one day. The dried poromeric material was then subjected to Newark flex tests using 4 samples for each test. The results were compared to the control which was the untreated poromeric material. Table I gives the average results obtained.

1 Greater than 22.

The results of these tests are extremely pronounced in the greatly increased flex life, using the process of the present invention as illustrated by Examples 2 through 5. Using only 0.5 percent lubricant, the flex life is increased almost five fold. In Examples 4 and 5, the testing was discontinued at 22 million flexes. It was readily apparent that the flex life was greatly in excess of the 22 million mark. It was also noted that the lubricant did not detrimentally aflFect the feel of the poromeric at about the one percent oil level or lower. At the 1.5 percent level, a slight oily feel could be detected but this was not deemed to be detrimental to the product.

EXAMPLES 6 THROUGH 14 TABLE II Percent by weight Percent oil of General Elecpickup by trio SF-1034 siliweight of Flex life cone polymer in poromeric (millions methylethylketone material of flexes) Example number:

6 (control) 0 0 3. 8 7 0.05 0.05 5.1 0. 1 0. 1 6. 3 0. 3 0. 3 6. 6 0. 5 0. 5 9. 0 1. 0 1. 0 9. 3 2.0 2.0 ll.0 4. 0 4. 0 l7. 8 5. 0 5. 0 21. 2

It is readily sene that even on the application of very small amounts of silicon oil, the flex life is improved. As compared to Examples 1 through 5, it was noted that larger amounts of silicon oil were required to effect a comparable increase in the flex life.

EXAMPLES 15 THROUGH 20 In these examples, another silicon oil was used to increase the flex life of the poromeric material prepared in accordance with Examples 6 through 14. Again, the silicon oil was diluted in methylethylketone as noted in Table III. The silicon oil used was Dow Corning 1109 having a viscosity of 5-8 centistokes at room temperature. The results obtained are shown in Table III.

TABLE III Percent Dow Corning 1109 It will be readily noted that while 0.1 percent of the silicon oil about doubled the flex life, greater amounts did not greatly increase the flex life. Therefore, this silicon polymer is highly desirable to effect a doubling of the flex life with a minimum addition of lubricant.

In the same manner, other silicon oils may be used with nonwoven fibrous substrates as well as with other flexible substrates such as woven, knitted and the like fabrics as well as flexible polymeric sheet material with correspondingly good results. In addition, other lubricants, particularly petroleum motor oil of S.A.E. 5W to 70, synthetic hydrocarbons of molecular weights in the range of 250 to 50,000, fatty monoesters, glycols, glycerides and their respective acids, amides, alcohols, nitrates, soaps, salts, epoxies are used either alone or as additives to basic lubricants with correspondingly good results.

While there have been described various embodiments of the present invention, it is understood that various changes therein can be made without departing from the scope of the invention. It is therefore intended to cover the invention broadly being limited only by the appended claims.

What is claimed is:

1. A poromeric material comprising a Water-vapor permeable, nonwoven needle punched bonded fibrous substrate coated with a water-vapor permeable polyurethane elastomer, said poromeric material being impregnated with from about 0.01 to about 10 percent by weight of a substantially nonvolatile lubricant, said lubricant being substantially free from solvent.

2. The poromeric material of claim 1 wherein said lubricant is a petroleum oil.

3. The poromeric substrate of claim 1 wherein said lubricant is a silicone oil.

4. The poromeric material of claim 1 impregnated with from about 0.05 to about 2 percent of said lubricant.

5. The process of increasing the flex life of a poromeric material which comprises a water-Vapor permeable, nonwoven rieedle punched bonded fibrous substrate coated with a water-vapor permeable polyurethane elastomer, said process comprising dissolving from about 0.01 to about 10 percent of a lubricant in a solvent to produce a lubricant solution, applying said lubricant solution to said poromeric material and penetrating into said material in an amount of about 0.01 to 10 percent lubricant based on the weight of poromeric material and subsequently removing said solvent from said poromeric material.

6. The process of claim 5 wherein the lubricant'is a petroleum oil.

7. The process of claim 5 wherein. the lubricant is a silicon oil.

(References on following page) 9 References Cited UNITED STATES PATENTS Cheronis et a1 117135.5 'Somerville 117135.5 Aoki 156-79X Heyden et a1. 1l7135.5X Chandler 117-135.5X Larner et a1. 161156 10 3,387,989 6/1968 West et a1. 117-76 ROBERT F. BURNETT, Primary Examiner W. A. POWELL, Assistant Examiner US. Cl. X.R. 

